Motor fuel



Patented Nov. 9, 1943 MOTOR FUEL Melvin M. Holm, San Francisco, Calif.,assignor to Standard Oil Company of California, San Francisco, Calif., acorporation of Delaware No Drawing. Original application May 31, 1939,Serial No. 276,623, now Patent No. 2,228,662, dated January 14, 1941.Divided and this application December 16, 1940, Serial No. 370,353

9 Claims.

This application is a division of my copending application Serial No.276,623, filed May 31, 1939, now United States Patent No. 2,228,662.

This invention relates to the addition of certain esters to motor fuelsconsisting essentially of branched chain paramn hydrocarbons and havinga relatively high antiknock value to increase the antiknock qualitythereof.

One object of this invention is to make motor fuels for internalcombustion engines, especially for aviation engines, which fuels haveantiknock values hitherto unobtainable without theuse of relatively highconcentrations of such metalloorganic antiknock agents as leadtetraethyl and iron carbonyl.

Another object is to increase the ant'iknock value of motor fuelsconsisting essentially of branched chain paraflin hydrocarbons andhaving initially a relatively high antiknock value and simultaneously toimprove the volatility or distillation characteristics of such motorfuels.

Another object is to provide motor fuels consisting essentially ofbranched chain paramn hydrocarbons having antiknock values higher thanany heretofore known for such fuels.

Still another object is to provide motor fuels particularly adapted foruse in aviation engines of the liquid-cooled or air-cooled type. e

Other objects will be apparent to those skilled in the art from thedisclosure of my invention which follows.

The unusually high antiknock quality of the branched chain parafiinhydrocarbons, such as 2,2,4-trimethyl pentane for example, has beenrecognized for years, but until very recently pure branched chainparaflln hydrocarbon compounds having such relatively high antiknockvalues were little more than laboratory curiosities. However, within thepast two or three years polymerization processes have been developedwhich convert gaseous olefins such as propylene, l-butene, and isobuteneinto branchedchain liquid olefins, which in turn may be converted to therelatively high antiknock paraflln's of corresponding structure bydirect hydrogenation. Also, more recently, these relatively highantiknock branched chain paraflln hydrocarbons have been produced byalkylation. Since the 7 development of these processes of polymerizationhigh antiknock relatively pure branched chain liquid paraflins havebecome commercially available and are sold as iso-octane or hydroctane."

This iso-octane or hydroctane".of commerce, however, even though havinga relatively high antiknock value, usually is not alone a satisfactorymotor fuel, for it is usually necessary that more volatile constituents,such as natural gasoline for example, be blended with it to make a 10finished fuel having the desired volatility or distillation curve, sothat the fuel will have the desired characteristics relating tostarting, acceleration, etc. because the available, more volatileblending stocks themselves, such as natural gasoline, usually haverelatively low antiknock values, and

have the effect of lowering the antiknock value of the blend- Evenrelatively pure isopentane, which is probably the best availablevolatile blending agent with regard to antiknock value, fails to improvethe antiknockyalue of such base fuels to any appreciable extent, if at.all. Thus, in view of the difficulty of increasing the antiknock valueof such fuels while at the same time obtaining the desired volatility,it has been necessary to make up the deficiencies in octane number bythe use of such organo-metallic antiknock agents as lead tetraethyl.This problem has been especially difilcult in the cases in which, fromsuch commercial iso-octanes, motor fuels have been made which arerequired to meet the volatility and octane number specifications in thefield of aviation and racing, where, for example, octane numbers in therange of 90 to 100 and higher are demanded.

Although the use of small concentrations of such metallo-organicantiknock agents as lead tetraethyl and i'ron carbonyl may not beobjectionable, the use of high concentrations has certain recognizeddisadvantages, such as valve corrosion and spark plug fouling, forexample. Moreover, because of such disadvantages, many consumers limitthe concentration -of such antiknock agents to certain maximum figures,for example, 3 cc. of lead tetraethyl per gallon. Even if theconcentration of such antiknock agent were not limited byspecifications, the maximum octane number which can be obtainedtherewith in the final fuel is limited largely by the octane number ofthe fuel without the antiknock agent This blending is objectionablepresent, since it is well known that the first increment of suchantiknock agent added gives the major octane number increase and furtherincrements result in progressively smaller increases in octane number.Upon the continued addition of increments of such antiknock agent,eventually a point is reached, around to octane numbers higher than thatof the base fuel, at which further addition thereof is either withoutappreciable effect or is at least entirely uneconomical.

Thus, from the foregoing considerations it may be readily seen that theproblem of increasing the antiknock value of such base fuels as thoseconsisting essentially of branched chain paraflln hydrocarbons, such ashydrogenated polymers obtained by polymerization and hydrogenation andalkymers obtained by alkylation, which themselvesinitially have anunusually high antiknock value, and at the same time obtaining a motorfuel having the desired distillation characteristics, is an exceedinglydifficult one. This problem is especially acute in the field of aviationgasolines where antiknock values of 100 octane number and well above arenow being demanded. As a result of the limitations described above, thefuel manufacturer is forced to maintain high octane number values notonly on his commercial iso-octane but also on his more volatile blendingstock. However, even with the most careful expensive controls to obtainhigh antiknock standards both on the base fuel and on the volatileblending stock, the result, especially with regard to the simultaneousattainment of the required antiknock value and distillation curve, isnot as satisfactory as is desired.

I have now discovered that certain low-boiling esters are especiallysuited for blending with high octane motor fuels consisting essentiallyof branched chain paraffin hydrocarbons to increase the antiknockquality of such fuels. Not only do these esters give an unexpectedlyhigh increase in antiknock value to these motor fuels, which initiallyhave an unusually high'antiknock value, but also at the same time manyof them aid in producing a motor fuel having the desired volatility ordistillation characteristics and reduce, and in some cases eveneliminate, the proportion of volatile constituent which have an adverseeffect on or, fail to improve the antiknock value,

.such as natural gasoline or isopentane, which proportion is otherwiserequired to be blended with the base fuel to produce a fuel having thedesired volatility or distillation characteristics.

The esters which may be used according to this invention are thesaturated aliphatic esters of monocarboxylic acids, the esterscontaining from three to seven carbon atoms per molecule and boillngover the range from' 130 to 300 F. Examples are methyl acetate, methylpropionate, methyl normal butyrate, methyl isobutyrate,

, methyl valerate, methyl caproate, ethyl formate,

cule are preferred, the esters containing three carbon atoms permolecule may be used where higher volatility is desired and relativelyhigh water solubility and low heat of combustion are not undesirable,and esters containing six to seven carbon atoms per'molecule may be usedwhere relatively low water solubility and a high heat of combustion aredesirable and relatively low volatility oifers no problem.

The branched chain paraflln stocks used as base fuels, according to thisinvention, comprise those branched chain parafiins containing from fiveto twelve carbon atoms per molecule. amples are 3-m'ethyl pentane,2,3-dirnethyl pentane, 2,4-dimethyl pentane, 2,2,3-trimethyl butane,2,2-dimethyl hexane, 2,5-dimethyl hexane, 2,2,4-trimethyl pentane,2,2,3-trimethyl pentane, 2,3,4-trimethyl hexane, 2,2,4-trimethyl hexane,2,3,5-trimethyl heptane, neohexane, and 2,2-dimethyl butane. Thesecompounds are at present made by hydrogenation of the polymers usuallyobtained by the polymerization of normally gaseous olefinic hydrocarbonsor made by the alkylation of isoparafflns with normally gaseous oleiinichydrocarbons. However, the invention embraces the branched chainparaifin hydrocarbon compoundsv themselves and is not restricted to anyspecific method of their manufacture. Thus, al-.

though these stocks are frequently referred to as hydrogenated stocksfor convenience, the base fuels may be made by reactions involving nohydrogenation step. For example, a suggested above, theproducts obtainedby alkylation of isobutane and isopentane with propylene, normalbutenes, and isobutene in thepresence of sulfuric acid or aluminumchloride catalysts, are included within the scope of this invention.Furthcrmore, this invention embraces the addition of the esters to anyone, or a mixture of any two or more, of these branched chain paraffinhydrocarbon compounds containing from five to twelve carbon atoms permolecule. It is especially signiflcant that the best results areobtained when the branched chain base fuel has an octane number of atleast about 85 and may have an, octane number much higher, as high as100 in the case of 2,2,4-trimethyl pentane, for example, or above 100 inthe case of some of the other pure branched chain paraflin hydrocarbons.T

Furthermore, although I have found that branched chain parafilnhydrocarbons as a class give good results when in admixture with estersin accordance with this invention, thebest recontaining four-and fivecarbon atoms per molesuits are found to be obtained when the base fuelcontains substantial proportions of branched by hydrogenation or theprocesses of .alkylation mentioned above, the distinguishingcharacteristics of which branched chain parafl'ln hydrocarbons are thatthe .degree of branching is high, as indicated by the relatively highantiknock value of the base fuel. 'Such hydrocarbons as 2,4-dimethylpentane, 2,2,3-trimethyl butane, 2,2,4-trimethyl pentane, 2,2-dimethylhexane, 2,2,4-trimethyl hexane, and 2,3,5-trimethyl heptane illustratewhat is meant by hydrocarbons having a relatively high degree ofbranching. Such branched chain parafllns have at least two or three ormore side branches, and the greater the number of carbon atoms ingeneral the greater the number of side chains from the main straightchain. Such branched chain parainns having a high degreeof branching inthe mole- Specii'lc exor in mixtures thereof if desired, to obtain acompound havinga high antiknock value when' blended with esters inaccordance with this invention.

The proportion of esters added to the base fuel consisting essentiallyof branched chain paramn hydrocarbons will depend on the octane numberand volatility or distillation characteristics desired and should besuch that the ester comprises 10 to 50 per cent by volume of thefinished fuel. Proportions lower than 10 per cent may, of course, beused but I find that the blending octane numbers increase, in general,with increasing concentration, and the preferred improvement is notreached until about 10 per cent of the ester has been added. Blendscontaining proportions higher than 50 per cent may be used to obtain ahigh antiknock value, but are undesirable for some purposes because ofthe resulting relatively low heats of combustion of such final blends.

The hydrocarbon component comprising 50 to 90 per cent of the finishedfuel may be made.

up entirely of branched chain paraffln hydrocarbon stocks as describedabove, or entirely of one or more of the branched chain paraffinhydrocarbons also described above, or it may also contain substantialproportions, for example 10 to 50 per cent, of volatile blending stockssuch as natural gasoline. blending stock for this purpose is isopentane.Moreover, the high antiknock fuel of my invention may, of course, beblended with other motor fuels in the usual manner. v

In order toillustrate the invention, examples of motor fuels made up inaccordance therewith and data obtained from tests made thereon are givenin Table I below: I

TABLE I Base fuel-commercial iso-octane Oct. No. Vol. Blending Ester ofbase ester in oct. No

fuel blend of ester Methyl acetate 4 90.0 93.8 25 105.2 D 90.0 99. 7 50109. 4 Ethyl l'ormate 90.0 92.9 25 101.0 Ethgl acetate.-- 90.0 94. 9 25109.6 90. 0 100+ 50 110+ Isopropyl l'ormate. 90. 0 93. 9 25 105. 6 090.0 100 50 110.0 Isopropyl acetate 90. 0 94. 8 25 109. 2 0 90. 0 100+50 110+ Ethyl propionate. 90. 0 94. 8 25 109. 2 o 90.0 100+ 50 110+Secondary butyl acetate. 90. 0 93. 6 25 104. 4 Do 90. 0 97. 9 60 105. 8Tertiary butyl acetate-.- 90. 0 90. 2 .25 102. 8 Do 90.0 97.8 50 105.8

In Table I are given the octane number of the base fuel, the octanenumber of the blend, the volume per cent of ester in the blend, and the"blending octane number of the ester. The "blending octane number of theester" is obtained by multiplying the difierence between the octanenumber of the blend and the octane number of A particularly suitablevolatilemended by the Cooperative Fuel Research Committee of theAmerican Society for Testing Materials.

It'is apparent from the results set forth in Table I that by means of amixture of branched chain paraffln hydrocarbons and saturated aliphaticesters of monocarboxylic acids as disclosed herein, motor fuels may beobtained having antiknock values higher than any heretofore known forsuch base fuels. In each case in Table I the blending value is above 100for 25 volume per cent of the ester and, in each case where a test wasmade with per cent, the blending value for 50 per cent was greater thanfor 25 per cent, showing that the susceptibility of the branched chainparaffin hydrocarbons to increase in anti-knock value by the ester addedincreases with the proportion of ester added. In other words, theblending octane numbers of these esters increase with increasingconcentration. Thus, from the data here given it is seen that such a.fuel containing a large proportion of such ester has a very highanti-knock value, and its anti-knock value is higher than any known forsuch a base motor fuel. This is especially true of ethyl acetate andethyl propionate. Moreover, blending such esters with branched chainparaffln hydrocarbons having anti-knock value well above 90.0 octanenumber, as high as 100 as for 2,2,4-trimethyl pentane, for example, oreven above 100, will give still higher antiknock value. No figures canbe given to indicate the octane number of these fuels having ananti-knock value above 100 octane number, be-

cause no test has been devised for compounds v creased by the additionof a small concentration of such a metallo-organic anti-knock agent aslead tetraethyl.

The examples in Table I are cited to illustrate the effect of the'esterson anti-knock value.

Although the compounds blended as indicated in Table I may be used asmotor fuels, usually the addition of some isopentane,- natural gasoline,or the equivalent, is required in order to meetthe usual gasolineboiling point specifications, the

although each of the specific examples given in Table I above indicatesthe use of a single ester, two or more esters may be added to the basefuel, and such compositionsare included in this invention. Furthermore,as indicatedabove, one branched chain paraffin hydrocarbon component ofthe base fuel may be used alone or a mixture of these components thereofmay be used.

Results obtained from tests on representative esters indicate that,although 'an increase in.

Tests II Oct. No. Vol. B Ester Base fuel of base gfi' m ester a cot. Nofuel V blend of actor Ethyl acetate Commercial lac-octane 90.0 94. 9 25109. 6 Do Stanavo base 76.3 80.8 25 94.3

Commercial 1mm 90.0 1 100+ so 1 110+ Unhydrogenated polymers 80. 3 89. 550 98. 7 Stanavo base I 76.8 91. 7 60 106.6

Secondary butyl acetate Commercial iso-octane 90. 0 93. 6 25 104. 4

Do Stanavo base 76. 3 82 4 25 100. 7

1 These values are indefinitely higher than the values given because ofthe impossibility of measuring octane number of the blend where thevalue is above 100.

In Table II above the gasoline designated Table II when the esters ofthis invention are added to gasolines having an anti-knock 'value' aboveabout 85 and consisting essentially of branched chain parafllnhydrocarbons, the antiknock value increase is surprisingly high ascompared with the increase found for other gasolines having a relativelyhigh anti-knock value of 75 to about 85 and not consisting essentiallyof branched chain paramn hydrocarbons- Table II above'also indicatesthat the esters as disclosed are effective in base fuels other thanthose in which they give such unusualresults, and this inventiontherefore comprehends the novel-blends of such esters with other basefuels to increase the anti-knock value thereof.

Although one of the objects of the invention 40 is to provide highoctane fuels containing little or no metallo-organic anti-knock agent, Ihave found that the blends herein described are readily The 20susceptible to further improvement in octane number by addition of suchan agent as lead tetraethyl. Thus, with the addition of a relativelysmall quantity of such metallo-organic anti-knock agents as leadtetraethyl extremely high anti-knock values can be obtained. It willtherefore be understood that motor fuels with or.

without such metallo-organic anti-knock agents are embraced by .thisinvention.

The term metallo-organic anti-knock agen 'f. is used herein with theintention that it include those organic compounds of metals, especially5 the metallo-alkyl compounds such as the well It is to be understoodspecific m branched chain paraffin hydrocarbons,

esters, and certain prcportionsof the comm.

ents of my new motor fuel have been disclosed fo the purpose ofillustration, my invention is not to be limitedthereby but includes' allmodifications.

therenf the scope of the appended claims high antiknock motor fuelcomprising a motor mel-hy'drocarbons of the type produced by thealkylation of isoparafflns with normally. gaseousjoi'e'flns anda-sufllcient proportion of isoapropyl formate effective to increasesubstantially Intiknock value of. said base fuel.

/ consisting essentially of isoparafllnic. 7

2. A high antiknock motor fuel comprising a base fuel consistingessentially of isoparafllnic motor fuel hydrocarbons of the typeproduced by the alkylation of isoparamns with normally gaseous oleflnsand from about 10 to about by volume of isopropyl formats to increasesubstantially .the antlknock value of said base fuel.

3. A high antlknock motor fuel as defined in claim 1 in which said basefuel consisting essentially of isoparamnic motor fuel hydrocarbons hasan antilmock value of at least about octanenumber without said isopropylformate.

4. A high antiknock motor fuel having an antiknock value above octanenumber comprising a base fuel consisting essentially of isoparafllnicmotor fuel hydrocarbons of the type produced .by the alkylation ofisoparaflins with normally gaseous olefins and a sufficient proportionof isopropyl formate effective to increase the antiknock value of saidbase fuel to above 100.

6. A high antiknock motor fuel comprising a base fuel consistingessentially of isoparafllnic motor fuel hydrocarbons of the typeproduced by the alkylation of isoparafllns with normally gaseousole'flns and a suflicient proportion of methyl acetate effective toincrease substantially the anti-knock value of said base fuel.

7. A high antiknock motor fuel comprising a base fuel consistingessentially of 'isoparafflnic motor fuel hydrocarbons of the typeproduced by the alkylation of isoparafl'lns with normally gaseousolefins and a sufficient proportion of secondary butyl acetate effectiveto increasesubstantially the antiknock value of said base fuel.

8. A high antiknock motor fuel comprising a base fuel-consistingessentially of isopa'rafllnic motor fuel hydrocarbons of the typeproduced by the alkylation of isoparamns with normally ester selectedfrom the group consisting of satufrated aliphatic esters of formic acidand acetic gaseous oleflns and a sufficient proportion of an acidcontaining three to seven carbon atoms and boiling within the range ofto 300 F. effective to increase substantially the antlknock value ofsaid base fuel.

a 9. A high antiknock aviation motor fuel com-' normally gaseous oleflnsand having an antiknock value above about 85 and a sufficient pro-'portion of an ester selectedfrom the group consisting of saturatedaliphatic esters of formic acid and acetic acid containing three toseven carbon atoms and boiling within the range of 130 to 300? F.effective to increase substantially the antiknocl: valuecf, said ln'tsefuel.

" 'MELVINLLHOLM.

